This invention relates to a ferroelectric liquid crystal device, and particularly to a ferroelectric liquid crystal with a good alignment of ferroelectric liquid crystal.
The liquid crystal devices so far used in watches, electronic pocket calculators, etc. are based mainly on the display according to the twisted nematic (TN) mode where the nematic liquid crystals are in a twisted structure, but the response speed is now limited to 20 milliseconds at the highest in this mode. On the other hand, display based on smectic liquid crystals has been actively tried, and particularly liquid crystals having a smectic C* phase, which may be represented also by Sm* C phase or called chiral smectic C phase, or a smectic H* phase, which may be represented also by Sm* H phase or called chiral smectic H phase, have been regarded as important owing to the ferroelectricity since Meyer et al discovered it [Le Journal de Physique-Letters 36, L 69 (1975)]. These liquid crystals were found to have a high speed response of less than 1 millisecond by Clark et al [Appl. Phys. Lett) 36, 899 (1980)] and new fields have been expected for these liquid crystals.
It is important that devices utilizing these ferroelectric liquid crystals must be aligned in some preferential directions in parallel to the substrate surface. The well known procedures for aligning the ferroelectric liquid crystals utilize an application of a strong magnetic field or a shear stress, but are less practical as a production process. Fukuda et al proposed an alignment from the spacer edge ["Shizen", July issue (1983), pages 36-46; "Optronics", September issue, (1983), pages 64-70], but the domain for uniform alignment is as narrow as 100 .mu.m from the edge and is practically not satisfactory.
On the other hand, the ferroelectric liquid crystal cannot have so far had a uniform alignment even by alignment used in the alignment of the conventional nematic liquid crystal or cholesteric liquid crystal such as oblique vapor deposition of silicon oxide (SiO) (Japanese Patent Publication No. 54-12067) or the so-called rubbing, i.e. rubbing of an organic polymer film with cloth, etc., in a specific direction (Japanese Patent Publication No. 55-10180), and thus there is a problem of poor contrast ratio.
A process for aligning a ferroelectric liquid crystal by using an imide-based polymer and applying an electric field thereto together has been proposed [Japanese Patent Application Kokai (Laid-open) No. 58-173718], where a PIQ (polyimidoisoindroquinazolinedione, trademark of a product made by Hitachi Chemical Co., Ltd., Japan) film is rubbed and a liquid crystal is once brought into an isotropic liquid state, and slowly cooled while applying a strong electric field thereto, thereby obtaining a uniform alignment.
To solve these problems, the present inventors have made extensive studies on the uniform alignment of a ferroelectric liquid crystal to be attained only by rubbing, as in case of the nematic liquid crystal of the conventional type, without any application of an electric field, and have found that a uniform alignment can be obtained without any application of an electric field when a specific organic polymer film is used as an alignment-controlling layer. The present invention is based on this finding.